The present invention relates to level adjustment systems, and in particular to level adjustment systems that level substrates.
In semiconductor manufacturing, a wafer is usually supported by a pin chuck to enable, for example, exposure of photolithography.
Referring to FIG. 1, a conventional pin chuck 1 comprises a base 11, an evacuation channel 12, a plurality of hollow pins 13 and two interferometer mirrors 14. The hollow pins 13 are uniformly formed on the base 11. The evacuation channel 12 is formed in the base 11 and is connected to the hollow interior of each hollow pin 13. The interferometer mirrors 14 are respectively disposed on two sides of the base 11 to position a wafer W.
As shown in FIG. 1, when the wafer W is placed on the base 11 and hollow pins 13, a vacuum pump 15 evacuates the evacuation channel 12. The bottom surface of the wafer W is thus securely attached to the base 11 and hollow pins 13. Exposure can then be performed on the top surface of the wafer W.
Referring to FIG. 2, another conventional pin chuck 2 comprises a base 21, an evacuation channel 22, a plurality of solid pins 23 and two interferometer mirrors 24. The solid pins 23 are uniformly formed on the base 21. The evacuation channel 22 is formed in the base 21 and under the solid pins 23. The interferometer mirrors 24 are respectively disposed on two sides of the base 21 to position a wafer W.
As shown in FIG. 2, when the wafer W is placed on the base 21 and solid pins 23, a vacuum pump 25 evacuates the evacuation channel 22. The bottom surface of the wafer W is thus securely attached to the base 21 and solid pins 23. Exposure can also be performed on the top surface of the wafer W.
The pin chucks 1 and 2, however, encounter a problem during processing of the wafer W. Although the wafer W can be securely attached to the pin chucks 1 and 2, the surface of the wafer W is usually uneven, whereby exposure is adversely affected or cannot be applied thereto.
For example, as shown in FIG. 3, a step-and-repeat or step-and-scan projection printing device 3 is above the pin chuck 1 and comprises a light source and illuminator 31, a mask 32 and an imaging lens 33. When the step-and-repeat or step-and-scan projection printing device 3 performs exposure on a photoresist layer 4 disposed on the top surface of the wafer W, the pin chuck 1 (or the pin chuck 1 and step-and-repeat or step-and-scan projection printing device 3) moves transversely. A distance D between the imaging lens 33 of the step-and-repeat or step-and-scan projection printing device 3 and the photoresist layer 4 on the wafer W, however, is usually short, such as between 1 and 10 mm. The change of D due to an uneven chucked wafer surface may cause the photoresist layer to be out of focus of the imaging lens 33.